Four component lens system for correcting curvature of field



350-469 SR SEARCH ROOM FOUR COMPONENT LENS SYSTEM FOR CORRECTING CURVATURE OF FIELDS April J. L. GREENSTEIN ETAL 2,467,667 I Filed July 11, 1946 R 7'2 d 3 R EAR OF PERISCOPE EYEPIECE LENS R REA R OF PERISOOPE EYEPIECE LENS INVENTORS. JESSE L.GREENSTEIN LOUIS G. HENYEY ATTORNEY Patented Apr. 19,1949

UNITED v STATES? PATE SEARCH ROON NT OFFICE FOUR COMPONENT LENS SYSTEM FOR COB- RECTING CURVATURE OF FIELD Jesse L. Greenstein and Louis G. Henyey, Williams Bay, Wis., assignor to the United States of America as represe the Navy nted by the Secretary of Application July 11, 1946, Serial No. 682,750 1 Claim. (cl. 38-57) own aberrations) the effective radius of the field is in the neighborhood of 35 millimeters. If the camera is focused ion the center of the field the curvature of field results in an out of focus image of about 0.35 millimeter size at an apparent field of 18 (the field of a conventional periscope is about 24 in radius). The natural curvature of field, called the Petzval curvature, Pz, arises even when the astigmatism is zero, because of the dominantly positive character of the lenses in a periscope. scopes it is not usually possible to eliminate the Pz.

The object of this invention is to provide an objective lens system which will correct not only its own curvature of field but an additional curvature of field such as that arising in a periscope.

The invention also resides in certain novel features of optical structure and arrangement which facilitate the carrying out of the foregoing object.

These results are obtained in the present device by using very steep divergent surfaces at points in the lens system where the bundle of rays is small and by placing the convergent surfaces at large heights on the bundle.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accom- Denying drawings in which:

Figure 1 shows an axial cross section of a lens system of the present invention.

Figure 2 shows a modification of the lens system.

While the invention is susceptible of various modifications and alternative arrangements, we have shown in the drawings and will herein describe in detail the preferred embodiments. It is to be understood, however, that we do not intend to limit the invention by such disclosure for we aim to cover all modifications and alternative arrangements falling within the spirit and scope of the invention as defined in the appended claim.

In Figure 1 the first or front element of the lens system which faces the rear vertex of the eye piece of the telescope is a collective lens L1 having a convex face R1, a thickness d1. and a concave A positive lens has positive P2; in peri- 2 face R2, whichis directed to the center of the system. The second lens element L2 is separated from the first by an air space s1 and has its convex face Ra facing toward the first element. The second element is of thickness d2 and its rearwardly directed face R4 takes up only a small central portion of the total cross section of the element. The third lens element consists of 3 lenses, the first of which L3 has its small concave face R5 directed forwardly and separated from the second element by an air space .92. This face R5 takes up only the central portion of the lens and has a diameter similar to that of R4. Lens 10 is smaller in diameter than lens L4 and has a thickness da. Its convex face Re is positioned in lens L4. Lens L4 has a center thickness (14 and a rearwardly directed concave face R1 which engages the forwardly directed face of lens L5 which v has a thickness ds and a rear convex surface Re.

The fourth lens element Ls is separated from the third by an air space sa. One convex face Ra faces forward. It has a thickness ds and the rear convex face R10 faces toward the film.

Optical data for the form of lens shown in Figure 1 15 as follows:

EXAMPLE Thickness Diameter Lens element Radius and at curved Separation surface Rear ciperiscope eye- Mm.

lens 17.2 mm.

R1= +24.7 mm. 31 L1 d1=4.0 31

R2=+44.1 mm.

' 8i=0.1 R|=+17.26 L: dz=18.0 25

a:=4.0 R5= -l2.52 5

L3 d3=s.5 11 p 5.89 L4 li4=3.7 25

- R +20.0 L; d5=11.8 25

. ar -0.1 R =+83.4 L. d=7.0 31 R1o= -38.5 31 A proximate back ocus 47.3

Glasses Index of Reciprocal refraction dispersion I a i 1 3. This lens has an equivalent focal length of 50 mm.

As may be seen from this description and the elements in the example, the exterior elements 4 v This lens has an equivalent focal length of 50 mm., a relative aperture of f/12, and covers a field of 48 diameter on a fiat film. The lenses are adapted for mounting on a 35 mm. camera.

L1 and Le have convergent surfaces which are What is claimed is: placed at large heights on the bundle of rays In afield-flattening lens system of 50 mm. focal and admit a large bundle of rays. Due to this length and U12 aperture for correcting the curvaconvergent action, the steeply divergent surfaces ture of a field of a preceding optical system/ com- R4 and Rs may be of relatively small diameter... prising lens elements having substantially the yet transmit rays at all the field angles supplied numerical data set forth in the following table by the periscope. By using these divergent surwherein L1, L2, designate successive elefaces, large negative P: can be obtained at the ments counting from the preceding optical sysexpense of relatively small loss in positive bendtem, R1, R2, radius of said elements, ing of the rays. Due to the convergent surfaces (11, d2, thickness and s1, s2, separation being placed at large heights on the bundle, at of said elements having index of refraction and net positive bending of the rays is possible along reciprocal of dispersion values as follows: with the strong negative Pz. Other aberrations are controllable and the astigmatism and lateral Thickness Ind Reciprocal color of the preceding telescope can also be- Emma"; Radius g f Refr tfim 1 altered in the camera lens. A field flattening an m on camera lens according to the present principles 172 mm to corrects its own Pz and two and a half times as preceding much more Pz arising in the periscope. L R 7mm 81mm It will be noted that the outer elements have l d1=4.o 1. 511 64.5 a lower index of refraction than the inner and that the thicknesses'of inner element L2 and lei-+1126 compound inner element L3, L4 and Lo are sub- RF+5 21 1-617 stantially thicker than those at the outer elea==4.o ments. 1., a,=e.5 1.611 58.8

A second example of a suitable lens shown in so Re=5.89 Figure is as folmws: L1 2' 1='3.7 1.617 36.6

1 R1=+20 Lens element Radius ifr i d 2 1 1 335 138,462; dFu's Separation surface R,=+33 4 I..- d =7.0 1. 517 64.5 I R10=-33.5 Rear of periscope 31.5mm...

eyelens. RH=+2OA mm. 20 JESSE L. GREENSTEIN- L11 R m LOUIS G. HEN'YEY.

"Hi-362 11-0 1 40 L" fin-+1431 dip-12.7 15 REFERENCES CITED P37 4 The following references are of record in the Rn=-12.44 c file of this patent: 13 R fl=6- 6 L w= 1 mam 34 UNITED STATES PATENTS L1: R17 =+20A d11=21 4 34 Number Name Date Rum-20.4 2,130,760 Warmisham Sept. 20, 1938 RPM 2,175,518 Djian Oct. 10, 1939 La R20 597 1u= goo Wa m s am July 13:1 Aklin Aug. 1 *rfiii back 2,363,788 Gottlieb Nov. 28, 1944 FOREIGN PATENTS Glasses Number Country Date Index of Reciprocal 423,468 Great Britain Feb. 1, 1935 refraction dispersion L11 L10 I. 517 64. 5 Ln L13 Lu 1- 611 58.8 L 1.617 36.6 

